1. Field of the Invention
The present invention relates to an image pickup apparatus equipped with an image sensing device such as a CCD (charge coupled device) with an interline structure, having the capability of individually reading all pixels.
2. Description of the Related Art
A CCD image sensor of the interline type is widely used as an image sensing device in a video camera. This type of CCD is composed of: an array of photoelectric conversion elements (pixels) for generating an electric charge in response to incident light; vertical transfer blocks (VCCDs) for reading the charges accumulated in the respective pixels and transferring the charges in a vertical direction; and a horizontal transfer block (HCCD) for transferring in a horizontal direction the charges received from the vertical transfer blocks. FIG. 14 is a layout of pixels 101 and a vertical transfer block 102 disposed on a CCD chip of the interline type. As shown in FIG. 14, the vertical transfer block 102 includes a plurality of transfer gate electrodes 103 wherein two transfer gate electrodes 103 are disposed at a position corresponding to each pixel 101. One of the two transfer gate electrodes 103 is formed at a position more closely adjacent to the corresponding pixel 101. When a charge transfer pulse is applied to the transfer gate electrodes 103, a charge is transferred into the vertical transfer block 102 via the transfer gate electrode 103 closer to the pixel 101.
The conventional interline-type CCD is designed for use in a video camera for taking a moving picture. For that purpose, an image signal is output basically according to the field-reading scheme in which all pixels 101 are read during each field period and the charges read from two pixels located at adjacent positions along the vertical direction are added together before being output. The combination of pixels to be added together is varied in an interlaced fashion between even-numbered fields and odd-numbered fields. That is, in even-numbered fields, the upper two pixels of the four pixels 101 shown in FIG. 14 are added together and the lower two pixels are also added together wherein the addition is performed in the vertical transfer block 102. In odd-numbered fields, on the other hand, the two pixels in the middle of the four pixels 101 shown in FIG. 14 are added together. However, the vertical resolution of this type of CCD is one-half that of a CCD of the frame-reading type in which pixel charges are directly output without being added. Thus, the conventional interline-type CCD cannot provide a high resolution required to take a still picture.
To solve the above problem, an interline-type CCD having the capability of individually reading all pixels 101 each field period and producing one frame of image signal from non-added pixel values within one field period has been proposed. FIG. 13 is a layout of pixels 101 and a vertical transfer block 102 disposed on a CCD chip. In this CCD, as shown in FIG. 13, transfer gate electrodes 103 are disposed in a vertical transfer block 102 so that three transfer gate electrodes are located at a position corresponding to each pixel. This arrangement makes it possible to read full frame data during one field period without a reduction in the vertical resolution due to the addition of charges performed in the vertical transfer block 102.
However, if a CCD of the type shown in FIG. 13 is employed in an image pickup apparatus, although it becomes possible to separately read charges from all pixels 101 during one field period, the three-transfer-gate structure of the vertical transfer block 102 makes it impossible to add two pixels along the vertical direction which is possible in the case of the CCD shown in FIG. 14. This means that, in the image pickup apparatus with the CCD having the full frame reading capability, such as that shown in FIG. 13, it is impossible to directly obtain a field signal of a moving picture.
Therefore, in the image pickup apparatus of the above-described type, after reading a frame signal from the CCD, it is required to add pixel values along the vertical direction for all pixel values so that a field signal of a moving picture can be produced from the frame signal.
It is an object of the present invention to provide an image pickup apparatus equipped with an interline-type image-sensing device, having the capability of individually reading all pixels thereby directly obtaining a field signal of a moving picture.
According to an aspect of the present invention, there is provided an image pickup apparatus, equipped with an interline-type image-sensing device, the image-sensing device including: a plurality of photoelectric conversion elements; a vertical transfer block for transferring the charges received from the photoelectric conversion elements along one direction, the vertical transfer block including transfer electrodes disposed in such a manner that at least three transfer electrodes are disposed for each photoelectric conversion element; and a horizontal transfer block for transferring the charges received from the vertical transfer block along a direction crossing the above-described one direction; wherein the charges read from the photoelectric conversion elements on a plurality of lines located at adjacent positions along the above-described one direction of the image-sensing device are successively transferred through the vertical transfer block so that the charges read from the photoelectric conversion elements on the plurality of lines located at adjacent positions along the above-described one direction of the image-sensing device are added together in the horizontal transfer block thereby outputting the added pixel signal.
According to another aspect of the present invention, the image pickup apparatus further includes mode switching means for switching the driving mode of the image-sensing device, the mode switching means being adapted to switch the driving mode so that the image-sensing device is driven either in a still picture mode or in a moving picture mode, wherein in the still picture mode one frame data is output during one field period, the frame data being produced on the basis of the charges read from the photoelectric conversion elements in which no addition is performed between the charges read from two photoelectric conversion elements located at adjacent positions along the above-described one direction, while in the moving picture mode, field data is output, the field data being produced on the basis of the charges read from the photoelectric conversion elements in which the charges read from two photoelectric conversion elements located at adjacent positions along the above-described one direction are added together.
According to still another aspect of the invention, the above-described moving picture mode comprises at least either:
a normal moving picture mode in which the addition operation of adding the charges read from two photoelectric conversion elements located at adjacent positions along the above-described one direction is performed once during each horizontal blanking period thereby outputting one field data during one field period; or
a high-speed moving picture mode in which the addition operation of adding the charges read from two photoelectric conversion elements located at adjacent positions along the above-described one direction is performed twice during each horizontal blanking period thereby outputting one field data during a half field period.
According to a further aspect of the invention, in the moving picture mode, the addition of the charge between two photoelectric conversion elements is performed in such a manner that the combination of two photoelectric conversion elements is interlaced between odd-numbered fields and even-numbered fields.
According to another aspect of the invention, the driving pulse for driving the horizontal transfer block has an amplitude corresponding to the number of photoelectric conversion elements whose charges are added together after being read.
According to a further aspect of the invention, there are provided a plurality of horizontal transfer blocks which are constructed so that charges may be transferred among these horizontal transfer blocks, and the driving pulse for driving said plurality of horizontal transfer blocks and the driving pulse for controlling the transfer operation among these horizontal transfer blocks have an amplitude corresponding to the number of photoelectric conversion elements whose charges are added together after being read.
According to still another aspect of the invention, of the plurality of horizontal transfer blocks, a horizontal transfer block located at a position furthest from the vertical transfer block has the capability of adding charges, wherein that horizontal transfer block at the furthest position has a transfer capacity greater than the other horizontal transfer blocks.
According to another aspect of the invention, the charges read from two photoelectric conversion elements located at adjacent positions along the above-described one direction are added together in the final stage of the vertical transfer block.
According to still another aspect of the invention, in the moving picture mode, one field data is produced by means of synthesis from two successive field data based on different amounts of exposure of light incident on the photoelectric conversion elements.
According to another aspect of the invention, in the synthesis process, when the exposure of the field data based on a greater amount of exposure than the other field data is within the range in which no saturation occurs, this field data is employed as the output field data while when the exposure of the field data based on a greater amount of exposure than the other field data is within the range in which saturation occurs, the field data based on a smaller amount of exposure is multiplied by a predetermined factor and the resulting multiplied data is employed as the output field data.
According to another aspect of the invention, the amount of exposure to the photoelectric conversion elements is controlled by controlling the exposure time by means of an electric shutter in which the charges accumulated in the photoelectric conversion elements are swept out toward a substrate.
According to a further aspect of the invention, in the moving picture mode, one output field data is produced by combining two successive field data which are shifted from each other.
The present invention having the aspects described above provides various advantages and features as will be described below. That is, the charges read from a plurality of photoelectric conversion elements located at adjacent positions along the above-described one direction are successively transferred through the vertical transfer block into the horizontal transfer block so that the charges are added together, and thus it is possible to obtain a field signal of a moving picture directly from the image-sensing device.
Furthermore, the image-sensing device can be driven in a desired mode selected from among three modes: a still picture more; a normal moving picture mode; and a high-speed moving picture mode. This allows the image pickup apparatus to be used in various manners according to the purpose of taking the picture.
Furthermore, the addition operation associated with the pixel charges is performed in an interlaced manner between odd-numbered fields and even-numbered fields and thus it is possible to obtain a high-quality moving picture.
Still furthermore, the amplitude of the driving pulse for driving the horizontal transfer block is increased in response to the number of photoelectric conversion elements whose charges are added together so that the horizontal transfer block has a large transfer capacity corresponding to the amount of charge to be transferred.
Furthermore, the driving pulse for driving the plurality of horizontal transfer blocks and the driving pulse for controlling the transfer operation among the plurality of horizontal transfer blocks have an amplitude corresponding to the number of photoelectric conversion elements whose charges are added together so that the transfer capacities within and among the horizontal transfer blocks are large enough to transfer the charges.
Furthermore, the addition of charges is performed in a horizontal transfer block located at a position furthest, of the plurality of horizontal transfer blocks, from the vertical transfer block. This allows a reduction in power consumption of the image-sensing device and also allows for simplification of the production process of the image-sensing device.
Still furthermore, the charges read from two photoelectric conversion elements located at adjacent positions along the above-described one direction are successively transferred so that the charges are added together in the final stage of the vertical transfer block. This makes it possible to obtain a field signal of a moving picture directly from the image-sensing device.
Furthermore, one field data is produced by means of synthesis from two successive field data based on different amounts of exposure of light incident on the photoelectric conversion elements so that the dynamic range is expanded.
Furthermore, the exposure time can be easily controlled by means of the electronic shutter.
Still furthermore, field data is produced by means of shifting pixel data so that a high-resolution image is obtained. Other objects, advantages, and features of the invention will become apparent from the following detailed description.